Method for manufacturing cooling unit comprising heat pipes and cooling unit

ABSTRACT

The present invention relates to a cooling unit for electronic devices wherein the manufacturing method comprises the steps of: (a) preparing a plate-type metal block for removing heat generated from an electronic component, the metal block having holes in the thickness part of the metal block and having convex portions formed on one main surface or both main surfaces of the metal block; (b) inserting heat pipes into the holes; and (c) applying a local and two-dimensional force from the surface of the metal block to the convex portions to make the surface flat bringing the outer surface of each heat pipe into close contact with the inner wall of each hole in the metal block.

This is a division of application Ser. No. 08/970,739 which was filed onNov. 14, 1997, now U.S. Pat. No. 6,122,138.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a coolingunit and the cooling unit comprising heat pipes for diffusing heatgenerated from electronic components or the like which has asemiconductor device and others mounted thereon and generates heat.

2. Description of the Related Art

As a means for preventing electronic equipment from overheating, aforced-air cooling system employing an air-cooled fan has been adopted.However, in high-density packaging electronic equipment typified byrecent computers, heat generated by the equipment tends to prominentlyincrease because of the high density of heat generating components suchas integrated circuits (IC) or large scale integration (LSI) mounted inthe equipment, and the cooling system using the air-cooled fan has alimited cooling capability.

Further, with the rapid advance of reducing the size of electronicequipment, a space for mounting the cooling unit becomes smaller withinthe equipment, which makes heat diffusion in the electronic equipmentdifficult.

As a countermeasure for solving such problems, there has been proposed amechanism by which heat generated by electronic components or electronicdevices (referred to as electronic components hereinafter) is receivedby a heat conductor and that heat is then removed from the electroniccomponents. Such a mechanism is partially put into practical use.According to this method, a heat conductive plate or the like is broughtinto contact with the electronic components which must be cooled downand heat of the electronic components is diffused to the plate or thelike to suppress excessive increase in temperature of the electroniccomponents. Moreover, the heat diffused to the plate or the like isfurther diffused in the electronic equipment or discharged outside theelectronic equipment if necessary.

When bringing the heat conductor into contact with a specific electroniccomponent for the purpose of cooling, it is desired to increase thevolume of the heat conductor to enlarge the heat capacity thereof and toincrease the area of the heat conductor which is brought into contactwith the electronic component to increase the speed of transferring heatfrom the electronic component. However, because minimization ofelectronic components have been advanced in recent days, the contactarea of such components relative to the heat conductor is limited, anduse of the cooling unit having a large volume is impossible.

A method for enhancing heat diffusion by attaching heat pipes to theheat conductor has been, therefore, proposed. Working liquid thatrepeatedly evaporates and condenses is sealed inside the heat pipe, andheat generated from the electronic component is transferred to anevaporation part of the heat pipe. The evaporated working liquid is thenmoved to a condensation part to condense in order to discharge heat.Excellent heat dissipation can be realized because the speed of theworking liquid is extremely high.

FIGS. 14 through 16 show an example of a conventional cooling unitutilizing such heat pipes. FIG. 14 is a plan view showing a conventionalcooling unit; FIG. 15 is a partially enlarged cross-sectional view takenalong line A—A of FIG. 16; and FIG. 16 is a front view of the coolingunit. This cooling unit constitutes heat pipes 1 each of which has aflat cross section and has an outer diameter of approximately 2 mm inthe vertical direction that transverses the length of the pipe and anouter diameter of approximately 4 mm in the horizontal direction thattransverses the length of the pipe, a metal block 2 attached to anevaporation part 10 of each heat pipe 1, and radiation fins 3 disposedto a condensation part 11 of each heat pipe 1. As for the metal block 2,aluminum or aluminum alloy is generally used for reducing the weight andsize of the cooling unit. Attachment of the heat pipe 1 to the metalblock 2 in the evaporation part 10 is achieved by forming a pipeinsertion hole 21 slightly larger than the flat heat pipe 1 in the metalblock 2 in the direction of the thickness and inserting the flat heatpipe 1 into the pipe insertion hole 21 as shown in FIG. 15. Solderingmetal 20 is subsequently poured into a gap between the surface of theheat pipe and an inner wall of the insertion hole 21 for integration.

In this-configured cooling unit comprising heat pipes, the main backsurface of the metal block 2 is brought into contact with each heatgeneration component 5 such as an LSI on a printed board 7 through ahigh heat conductive rubber 6 having a good heat conductivity, and themetal block 2 is attached to the printed board 7 in this state. Heatgenerated in the heat generation components 5 heats the evaporation part10 of each heat pipe 1 to evaporate the working liquid sealed inside thepipe 1. This increases the vapor pressure in the evaporation part 10 ofthe heat pipe 1 so that a vapor flows toward the condensation part 11where the pressure is low. Heat from the vapor moves to the condensationpart 11 and is transferred to the radiation fins 3 and diffused in theair. Accordingly, it is possible to obtain a relatively-small coolingunit having an extremely-high radiation performance.

The metal block 2 and the evaporation part 10 of each heat pipe 1 in theabove-described cooling unit are provided with heat pipes that are fixedby means of the solder alloy 20 as mentioned above. However, when thematerial of the metal block is aluminum or aluminum alloy, an oxide filmforms on the surface of the metal block preventing the soldering metalfrom being attached thereon and a void or bubble is generated betweenthe surface of the heat pipe and the inner wall of the insertion hole,and the heat resistance between the heat pipe and the metal blockbecomes large, thereby lowering the cooling characteristic of the unit.Furthermore, the pipe insertion hole must be made large to increase theamount of the solder to be poured therein in order to suppressgeneration of the void and fix the heat pipe in the pipe insertion hole.In this case, because the large specific gravity of the solder metalincreases the weight of the cooling unit and enlarges the insertionpipe, the thickness of the metal block must also be increased, andreduction in the thickness of the cooling unit can not be achieved.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a methodfor manufacturing a cooling unit comprising heat pipes which reduces thethickness of the metal block resulting in lighter weight of the entireunit and decreased heat resistance when connecting the metal block withthe heat pipes to achieve excellent heat dissipation or heat removalperformance and to provide a cooling unit.

According to a first embodiment of the present invention, there isprovided a cooling unit manufacturing method comprising the steps of:

(a) preparing a substantially-plate-type metal block for removing heatgenerated from an electronic component, the metal block having holes inthe thickness of the metal block into which heat pipes are inserted andhaving convex portions formed on one main surface or both main surfacesof the plate-type body corresponding with the holes;

(b) inserting the heat pipes into the holes for removing heat of themetal block; and

(c) applying local and two-dimensional force from the surface of themetal block to the convex portions to make the surface substantiallyflat after inserting the heat pipes into the holes and bringing theouter surface of each heat pipe into close contact with the inner wallof each hole in the metal block.

According to a second embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein each hole intowhich the heat pipe is inserted has a substantially circular crosssection and the heat pipe has a substantially circular cross section.

According to a third embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein each of theconvex portions has a substantially rectangular or trapezoidal crosssection.

According to a fourth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein each of theconvex portions has a substantially triangular cross section.

According to a fifth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein each of theconvex portions has a cross section substantially shaped corresponds toa combination of a trapezoid and a triangle.

According to a sixth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein the metal blockis made of aluminum or aluminum alloy.

According to a seventh embodiment of the present invention, there isprovided a cooling unit comprising the metal block and heat pipesproduced by the above manufacturing method.

According to an eighth embodiment of the present invention, there isprovided a cooling unit manufacturing method comprising the steps of:

(a) preparing a substantially-plate-type metal block for removing heatgenerated from an electronic component, the metal block having holes inthe thickness of the metal block into which heat pipes are inserted andhaving U-shaped grooves each provided with protruding portions on atleast one main surface or both main surfaces of the plate-type bodycorresponding with the holes;

(b) providing heat pipes in the U-shaped grooves for removing heat ofthe metal block; and

(c) applying local and two-dimensional force from the surface of themetal block to the protruding convex portions to make the surfacesubstantially flat after mounting the heat pipes on the U-shaped groovesand to bring the outer surface of each heat pipes into close contactwith the inner wall of each hole in the metal block.

According to a ninth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein each of theholes in which the heat pipes are inserted has a substantially circularcross section and each of the heat pipes has a substantially circularcross section.

According to a tenth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein convex portionsare further formed on the other surface with which the U-shaped grooveshaving the protruding portions from the main surface correspond.

According to an eleventh embodiment of the present invention, whereineach of the further-formed convex portions has a substantiallytrapezoidal shape.

According to a twelfth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein the metal blockis made of aluminum or aluminum alloy.

According to a thirteenth embodiment of the present invention, there isprovided a cooling unit comprising the metal block and the heat pipeswhich are produced by the above manufacturing method.

According to a fourteenth embodiment of the present invention, there isprovided a cooling unit manufacturing method comprising the steps of:

(a) preparing a substantially-plate-type metal block for removing heatgenerated from an electronic component, the metal block having holes inthe thickness part of the metal block into which the heat pipes areinserted and having convex portions formed on one main surface of themetal block corresponding to the holes;

(b) inserting the heat pipes into the holes for removing heat from themetal block; and

(c) applying local and two-dimensional force to the surface of the metalblock to the convex portions to make the surface substantially flatafter inserting the heat pipes into the holes and to bring the outersurface of each heat pipe into close contact with the inner wall of eachhole in the metal block.

According to a fifteenth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein each of theholes into which the heat pipes are inserted has a substantiallycircular shape and each of the heat pipes has a substantially circularshape.

According to a sixteenth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein each of theconvex portions has a substantially trapezoidal or rectangular shape.

According to a seventeenth embodiment of the present invention, there isprovided the cooling unit manufacturing method, wherein the metal blockis made of aluminum or aluminum alloy.

According to an eighteenth embodiment of the present invention, there isprovided a cooling unit comprising the metal block and the heat pipeswhich is produced by the manufacturing method comprising the steps of:

(a) preparing a substantially plate-type metal block for removing heatgenerated from an electronic component, the metal block having a hole inthe thickness of the metal bock and having a convex portion formed onone main surface of the metal block corresponding to the hole;

(b) inserting a heat pipe into the hole for removing heat from the metalblock; and

(c) applying local and two-dimensional force from the surface of themetal block to the convex portion to make the surface substantially flatand to bring the outer surface of each heat pipe into close contact withthe inner wall of each hole in the metal block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B illustrates a cooling unit according to an embodiment of thepresent invention;

FIGS. 2A-C illustrates various cross sections of a heat pipemanufactured according to the present invention after pressure has beenapplied;

FIGS. 3A-B illustrates the cooling unit having convex portions formed onboth surfaces of a metal block according to another embodiment of thepresent invention;

FIGS. 4A-C illustrates cross sectional views of the cooling unit havingtriangular convex portions on both surfaces, trapezoidal convex portionson one surface and triangular convex portions on the other surfaceaccording to still another embodiment of the present invention;

FIGS. 5A-C illustrates a further embodiment of the present inventionwherein groove portions into which the heat pipes are inserted areU-shaped grooves having the convex portions protruding from the surface;

FIGS. 6A-B illustrates cross-sectional views showing differentarrangements of the U-shaped grooves;

FIGS. 7A-B illustrates a cooling unit according to a further embodimentof the present invention wherein the convex portions are provided ononly one main surface of the metal block;

FIGS. 8A-C illustrates cross-sectional views of various heat pipes ofthe embodiment shown in FIG. 7A-B;

FIG. 9 illustrates a perspective view of a method for manufacturing thecooling unit according to another embodiment of the present invention;

FIGS. 10A-B illustrates a manufacturing method according to theembodiment shown in FIG. 9;

FIG. 11 is a perspective view of a test sample assembled for testing theeffect of the cooling unit according to the present invention;

FIG. 12 is a perspective view showing a prior art cooling unit;

FIG. 13 is a skematic view of a method for testing the effect of heatremoval of the cooling unit;

FIG. 14 is a plan view of a prior art cooling unit;

FIG. 15 is a plan view illustrating a connection between the metal blockand the heat pipe in the prior art cooling unit; and

FIG. 16 is a cross-sectional view showing a prior art cooling unit.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT OF THEINVENTION

The present invention will now be described in detail with reference tothe accompanying drawings. In the following description, a heat pipe hasa circular cross section with a diameter that ranges from 2 to 5 mm anda rod type heat pipe having a length of approximately 50 to 200 mm andbeing made of copper or aluminum. Further, a metal block is usually madeof aluminum or aluminum alloy to reduce weight.

According to the present invention, FIG. 1(b) shows one embodiment of acooling unit provided with heat pipes. A metal block 2 is a plate whichis made of aluminum or aluminum alloy and has outer dimensions of100×200 mm and a thickness of 3 mm. Each copper heat pipe 1 has an outerdiameter of 3 mm. As shown in FIG. 1, the part of the heat pipe 1 thatis inserted into the metal block 2 is flat while the part of the heatpipe 1 which is outside the metal block 2 being circular. As shown inFIG. 16, fins 3 are provided at one end of each heat pipe 1 by blurringfor the purpose of heat dissipation and are attached to the heat pipe 1by caulking.

A description will now be given as to a method for fixing the heat pipes1 to the metal block 2. The shape of the metal block 2 made of aluminumhas a thickness t₁ equal to 3 mm at a portion where no heat pipe 1 isinserted, and substantially trapezoidal or rectangular convex portions15 each of which has a width of t₂ equal to 4 mm and a height t₃ equalto 0.4 mm provided on the metal block 2 portions where the heat pipes 1are inserted in such a manner that the convex portions 15 are onopposing surfaces of the aluminum metal block 2. The metal block 2having such a shape can be manufactured by hot-pressing or abradingaluminum. A circular insertion hole having a diameter of 3.2 mm isformed in one cross section of the metal block and each copper heat pipehaving an outer diameter of 3 mm is inserted into the insertion hole. Atthis point in time, the heat pipe 1 has a circular cross section at theportion inserted into the hole.

In this state, the pressure of 40 kg/cm² is applied in both the upwardand downward directions, as shown by arrows in FIG. 1(a). Such amechanical pressure is preferably applied to the convex portions 15 andthe inserted heat pipe is deformed to have a substantially flat shape asshown in FIG. 1(b). The type of deformation depends on values of thewidth t₂ or the height t₃ of the convex portion 15 or how the mechanicalpressure is applied. Although this shape is preferably flat such thatboth main surfaces are completely flat as shown in FIG. 2(a), no problemoccurs in the practical use even if the central part slightly projectsas shown in FIG. 2(b) or the central part is slightly concave as shownin FIG. 2(c). Further, if the main surface of the metal block 2 (thesurface wider than the side surface) is previously machined to have ashape conforming with that of the electronic component to be mounted,contact made between the metal block 2 and the electronic component canbe improved, thereby increasing the heat removal efficiency. FIG. 2(b)shows an embodiment in which the surface of the metal block that isthermally connected with at least the electronic component is desired tobe sufficiently smooth, and the main surface of the metal block 2 issmoothed by pressure application using a press or the like or abrasionor other methods if necessary. This maintains good contact with theelectronic component which should be cooled down, thus realizing highperformance. It is to be noted that FIG. 1 shows a case where the numberof heat pipes used is three wherein the number and the interval betweenthe respective pipes can be appropriately determined by taking thenumber of electronic components to be cooled down and the quantity ofgenerated heat into account.

As mentioned above, the cross section of the heat pipe 1 inserted intothe metal block 2 is deformed to have a substantially-flat shape byapplication of mechanical pressure, the flat plane of thesubstantially-flat shape is pressed against the inner wall of the metalblock 2 with very strong force to realize sufficient thermal contact,and the mean distance from the surface of the metal block 2 to the heatpipe 1 is shortened, thereby reducing the heat resistance in the heatconduction.

FIG. 3(a) shows a variation of the first embodiment according to thepresent invention, which is similar to the above example in that eachconvex portion 15 is provided on both surfaces of the metal block 2 atthe portion where the heat pipe is inserted into the metal block butdifferent from the example shown in FIG. 1 in that the thickness of themetal block 2 into which the heat pipe 1 is inserted is larger than theouter diameter of the heat pipe 1. That is, in the embodiment shown inFIG. 3, an outer diameter of the heat pipe 1 is 3 mm; the metal block 2has a thickness t₁ equal to 4 mm; the convex portion 15 has a width t₂equal to 4 mm and a height t₃ equal to 0.2 mm; and the insertion holehas an outer diameter of 3.2 mm. If the thickness of the metal block 2is larger than the outer diameter of the heat pipe 1, as it is in thisembodiment, it is desirable that the height of the convex portion 15 islarger than the gap between the insertion hole formed in the base metalblock and the outer diameter of the heat pipe 1 and that an area of thecross section of the convex portion 15 is larger than that of the gap.With the heat pipe 1 being inserted into the insertion hole as shown inFIG. 3(a), press working is performed to obtain a shape illustrated inFIG. 3(b). In this method, because the quantity of deformation caused bypressure application is small as compared with the example shown in FIG.1, pressing can be done at an ordinary temperature, and the time forapplying pressure can be advantageously shortened.

Although FIG. 3(a) shows an example where each convex portion 15 has asubstantially trapezoidal or rectangular cross section, the crosssection is not restricted to a substantially trapezoidal or rectangularshape. It may have, for example, a substantially triangular shape havinga width of 2 mm and a height of 0.5 mm as shown in FIG. 4(a). Also, theconvex portion on both surfaces of the metal block may have a crosssection which is a combination of a substantially trapezoidal orrectangular shape and a substantially triangular shape as shown in FIG.4(b). In addition, the convex portions 15 may be provided on bothsurfaces of the metal block 2 in such a manner that they are opposed toeach other as shown in FIG. 4(c), or the convex portions 15 may bealternately provided on both surfaces with respect to one heat pipe. Inthis case, because the quantity of deformation of the heat pipe issmall, such an arrangement is effective especially when the diameter ofthe pipe is small and often is adopted when securing the passage of theheat pipe working liquid.

FIG. 5 shows another embodiment according to the present invention. Asshown in FIG. 5(a), U-shaped grooves 17 for mounting the heat pipe 1 areformed on one surface of the metal block 2, and convex portions 15 areprovided on side parts of the grooves 17 while convex portions 16 eachhaving a substantially-trapezoidal or rectangular cross section areprovided on the other surface of the metal block 2. In this case, twoconvex portions 15 are formed on side portions of each groove whichpreferably have a cross sectional area larger than the differencebetween the cross-sectional area of the U-shaped groove and that of theheat pipe, i.e., the cross-sectional area A shown by notched lines inFIG. 5(c). In FIG. 5, an aluminum plate having a thickness of 5 mm isused as the metal block 2, an U-shaped groove 17 having a width of 3.2mm and a depth of 4 mm is formed on one surface of the plate, a convexportion 15 having a cross section of 1 mm×1 mm is provided on each ofthe side portions of the groove, and a convex portion 16 having a heightof 0.2 mm and a width of 2 mm is provided on the back surface of themetal block 2. The heat pipe 1 having an outer diameter of 3 mm ismounted in the U-shaped groove 17 of the metal block 2, and mechanicalforce is applied to the surface of the metal block 2 by using a pressmachine. As a result, the heat pipe 1 is deformed to have asubstantially flat shape and the heat pipe 1 and the metal block 2 arethermally and closely connected as shown in FIG. 5(b).

Although FIG. 5 shows the example in which the U-shaped groove 17 isformed on one surface of the metal block 2 while the convex portion 16is provided on the other surface of the metal block 2, the U-shapedgroove 17 and the convex portion 16 may be alternately arranged as shownin FIG. 6(a). Alternatively, only the convex portions 15 formed on theside portions of the U-shaped groove 17 may be employed without usingthe convex portions 16 formed on the other surface, as shown in FIG.6(b).

FIG. 7 illustrates yet another embodiment of the present invention. Inthis embodiment, substantially trapezoidal or rectangular convexportions are provided on one main surface of the metal block, and holesin which the circular heat pipes are inserted are formed in thecorresponding thick parts of the convex portions. After inserting theheat pipes into these holes, the metal block is pressed by, for example,a press so that a part of the circumferential portion of each heat pipebecomes flat. In this case, the cross section of each heat pipe isdeformed as shown in FIG. 8 depending on the degrees of the pressure orpressing employed by the method. The thermal contact achieved betweenthe metal block and the heat pipes is superior to that attained by thesolder alloy.

FIGS. 9 and 10 show another method for pressing the metal block suchthat the cross section of each heat pipe has a substantiallysemicircular shape. In this case, the circular insertion hole ispreviously formed in the plate-type metal block. A spacer is set at aposition where the heat pipe is inserted after inserting the heat pipehaving a circular cross section in order to give pressure using apressing machine. The circular heat pipe is then pressed to have asemicircular cross section as shown in the drawings, and the thermalcontact between the metal block and the heat pipe is improved.

The following describes the specific effect of the thermal contactbetween the metal block and the heat pipe in the embodiments accordingto the present invention.

FIG. 11 is a schematic view showing a cooling unit according to thepresent invention. The block 20 is made of aluminum (A1100, a JapaneseStandard for an aluminum alloy) and is a plate type having dimensions of50 mm×30 mm. This cooling unit was manufactured as follows. The blockhaving a hole with a diameter equal to 3.1 mm was formed. The block hasa thickness of 4 mm at a portion where the hole is formed and athickness of 2 mm at any other part. The copper heat pipe having adiameter of 3 mm, an overall length equal to 200 mm, a thickness equalto 0.3 mm, water was used as the working liquid, and a small grooveformed inside (not shown) was inserted into the hole. The part of theblock having a thickness of 4 mm was subsequently subjected to pressworking along the thickness direction so that the part of the block towhich the heat pipe was inserted had a thickness of 3 mm. As a result,the inserted heat pipe 1 was deformed to have a substantiallysemicircular shape, and the hole was also deformed to have asubstantially semicircular shape, as shown in FIG. 11. In this way, asample of the block 20 which is shown in FIG. 11 and attached to bothends of the heat pipe 1 having a length equal to 200 mm wasmanufactured.

As shown in FIG. 13, one sample block 20 a was soaked in hot water 24having a temperature of 60 degrees Celsius. Here, the heat pipe 1 wasmaintained so as to be substantially vertical for five minutes in such amanner that approximately 15 mm of the block 20 a was soaked in the hotwater. After five minutes, the block 20 a was taken out from the hotwater 24, and temperatures of the block 20 a and the metal block 20 b attheir central parts were rapidly measured and compared. The resultshowed that a difference between the temperatures of the block 20 a andthe block 20 b was 6 degrees Celsius.

COMPARATIVE EXAMPLE 1

As a comparative example, the plate-type aluminum block (A1100) havingno convex portion on the main surface and having the dimensions of 50mm×30 mm and the thickness of 4 mm was prepared. A hole was formed inthe block at a position similar to that of the example shown in FIG. 11,and the block was flattened by mechanical pressing after inserting theheat pipe into the hole, thereby producing the primary component of thecooling unit according to the present invention. The thickness of theblock, including the part into which the heat pipe is inserted, beforeapplying the mechanical press was uniformly 4 mm, but application of thepress changed the thickness to 3 mm. As a result, the heat pipe wasdeformed to have a substantially-elliptical shape at the part insertedinto the block.

The performance of this comparative example was similarly measured asthat of the first embodiment. The measurement showed that the differencein temperature between the metal blocks at both ends of the heat pipewas approximately 7 degrees Celsius. Compared with the first embodiment,although the heat capacity of the metal block is different to someextent, it can be noticed that the first embodiment realizes heatconduction property superior to that of comparative example 1.

EMBODIMENT 2

In this embodiment, a sample such as shown in FIG. 11 was produced bythe manufacturing method illustrated in FIG. 1. The specific dimensionsare the same as those described in connection with FIG. 1. It is to benoted that the block 21 is made of aluminum A1100 and is of a plate typehaving the dimensions of 50 mm×30 mm. One heat pipe was inserted into ahole having a diameter of 3.1 mm which was formed in the metal blockhaving a thickness of 4 mm and press working was applied. Theperformance evaluation of the cooling unit was similarly carried out asthat of the first embodiment and showed that a difference in temperatureof the blocks 21 provided on both ends of the heat pipe 1 was 7 degreesCelsius.

FIG. 12 is a perspective view schematically showing a primary componentof a conventional cooling unit. The block 22 is made of aluminum (A1100)and is of a plate type having the dimensions of 50 mm×30 mm. Thethickness of the block 22 is 4 mm. A heat pipe 1 and block 22 areconnected to each other by means of soldering. As to the manufacturingmethod, the melted solder alloy (composition: Sn/Pb=6/4) is filled in ahole having a diameter of 3.3 mm into which the heat pipe 1 is insertedwith the block 22 being set on edge. In this state, the heat pipe 1 isslowly inserted and the solder alloy is then set. As a result of theperformance evaluation similar to that effected in the first embodiment,it was found that a difference in temperature between the blocks 21provided at both ends of the heat pipe 1 was 8 degrees Celsius.

As is apparent from the results of the above-mentioned performanceevaluation of the primary component in the cooling unit, a difference intemperature between the blocks provided on both ends of the heat pipe issmall and the good thermal contact between the heat pipe and the blockis realized in the embodiments of the present invention. Therefore, useof the cooling unit according to the present invention as such a coolingunit shown in FIG. 1 enables the efficient heat removal or heatradiation from the electronic components. As compared with theabove-described prior art, the cooling unit according to the presentinvention can be readily manufactured and is advantageous in terms ofcost.

As explained above in detail, according to the present invention, theholes or U-shaped grooves for mounting the heat pipes are formed in themetal block for attaching a heat generation part of the electroniccomponent, the convex portions are provided in the metal block atpositions where the heat pipes are mounted, and the mechanical force isapplied using a pressing machine or the like after inserting the heatpipes in order to connect the heat pipes with the metal block. Thus, thecross section of each heat pipe is deformed to have a flat shape, andthe outer surface of each heat pipe is closely brought into contact withthe inner wall of each hole or each groove of the metal block to causeheat resistance to be prominently decreased at the contact part, therebyresulting in a cooling unit provided with heat pipes which has anextremely-high efficiency of heat radiation or cooling.

Further, because the metal block and the heat pipes do not have to beconnected by means of the solder alloy, the thickness of the metal blockcan be decreased, resulting in reduction in size and weight of thecooling unit. Furthermore, when at least one surface of the metal blockis made flat and smooth by machining, the heat generation part and themetal block are closely connected with each other, which enablesimprovement of the heat radiation or cooling characteristic.

What is claimed is:
 1. A cooling unit manufacturing method comprisingthe steps of: (a) preparing a substantially plate-type metal block forremoving heat generated from an electronic component, said metal blockhaving a U-shaped groove provided with a protruding portion from atleast one main surface or both main surfaces of the metal block; (b)inserting a heat pipe into said U-shaped groove for removing heat of themetal block; and (c) applying local and two-dimensional force from thesurface of the metal block to the protruding portion to make the surfacesubstantially flat and bringing each heat pipe into close contact withthe inner wall of each U-shaped groove in the metal block.
 2. A coolingunit manufacturing method according to claim 1, wherein said U-shapedgroove into which the heat pipe is inserted has a substantially circularcross section and the heat pipe has a substantially circular crosssection.
 3. A cooling unit manufacturing method according to claim 1,wherein a convex portion is further formed on the other main surface ofthe metal block at a location that corresponds to where the U-shapedgroove having the protruding portion is provided on the main surface. 4.A cooling unit manufacturing method according to claim 1, wherein saidconvex portion formed on the other main surface, to which the U-shapedgroove having the protruding portion correspond, has a substantiallytrapezoidal shape.
 5. A cooling unit manufacturing method according toclaim 1, wherein said metal block is made of one of aluminum andaluminum alloy.
 6. A cooling unit comprising the metal block and theheat pipe which is produced by the manufacturing method defined in claim1.